A major challenge in oil formulation is simultaneously achieving desired lubricant antifoaming performance and filterability in filtered applications.
Defoamants are added to lubricants to prevent foam generation in service. Foam is a concern of lubricant end users due to: interference with lubricant-level monitoring; concern over entrained air interfering with lubricant film thickness; cosmetic issues (foam is easily visible and can indicate contamination); potential for spill-over (slippery spots); and the like. In particular, foam is a significant concern in gear oils as it prevents accurate measurement of the lubricant level.
The current state of the art is the use of methylated silicones namely polydimethylsiloxanes (PDMSs). However, the PDMSs have a low refractive index, high density, high Si content, and are removed by common filter material (including cellulosic and glass fiber media).
Despite advances in lubricant oil formulation technology, there exists a need for an oil lubricant that can effectively achieve both good lubricant antifoaming performance and filterability in filtered applications.